Knowing the degree of firmness or ripeness of fruit or vegetables (in the following description and claims referred to for convenience simply as fruit) is a factor of considerable commercial importance as it enables importers and distributors, for example, to assess the shelf-life of the fruit and meet the requirements of supermarkets and other retail outlets in this regard. When picked, even fruit from the same tree or plant is of different ripeness and any assessment made at this time is unreliable. Thus, boxes of fruit picked at the same time contain fruit with different degrees of ripeness. After picking, fruit is stored and transported under refrigerated conditions in order to prevent further ripening. Prior to supply to a retail outlet, the importer or distributor removes the fruit from cold store and exposes it to a warm environment to ripen it. It is at this stage that it is important to be able to assess or measure the ripeness of the fruit so that the importer or distributor may control the ripening to the degree necessary for the fruit to be supplied to the retail outlet with the required shelf-life.
One current method of testing fruit, such as avocado pears, to investigate the ripeness is to use a penetrometer. This is a hand-held instrument which comprises a pin or spike for pushing into the fruit, and a force meter which detects the force required to push the spike into the fruit and, hence, the degree of ripeness. Another instrument devised by the industry for testing the ripeness of an avocado pear is a firmometer. This instrument utilises a lever for applying a fixed force to the exterior of the fruit and measures the resulting deflection of the lever to provide a reading indicative of ripeness. U.S. Pat. No. 5,315,879 describes a measuring apparatus which may be used for measuring the firmness of fruit and other objects and which operates on similar principles to a firmometer. Both the penetrometer and firmometer type of instrument have the disadvantage that they damage or bruise the fruit being tested so that, particularly, in the case of the penetrometer, the fruit tested becomes unsaleable. Hence, they are used for testing on a selective basis and do not enable each individual fruit to be tested and individually assessed for shelf-life and treated and/or packaged accordingly.
EP-A-0 267 737 describes apparatus for testing all fruit in a batch so as to measure individual ripeness. It makes use of a transducer comprising a polymeric piezoelectric film having electrodes and secured by adhesive to a metal plate which in turn is mounted on a resilient block of foam material. The fruit to be tested is caused to impact on the transducer which produces an electrical output from the film. The metal plate is selected so as to have a mass which is small in relation to that of the fruit and is made of a metal which is non-resonant under the impact. The foam support is such that the film, the plate and the fruit move in contact during the impact. This arrangement has the result that the output signal from the film represents the resonance of the fruit due to the impact, which can be used as a measure of the firmness or ripeness of the fruit.
WO094/29715 describes a method and apparatus for testing the quality of a fruit by applying a dynamic force to the fruit and detecting the mechanical response of the fruit by means of piezoelectric film transducers supported on a displaceable supporting member. Hence, in so far as it measures the mechanical response of the fruit, it is similar to EP-A-0 267 727.
EP-A-0 351 430 and U.S. Pat. No. 4,542,639 both relate to the impact testing of engineering structures, such as laminates or honeycomb constructions, for delaminations and desponds. In the arrangement of EP-A-0 351 430, a sensor is mounted on a hammer which imparts a non-destructive impact to a material which is to be measured, and a signal produced by striking the material with the hammer is used to indicate the period of time of contact of the hammer with the material. The impact drive force applied to the hammer is removed by using a signal from the sensor as soon as the hammer comes into contact with the material being measured. U.S. Pat. No. 4,542,639 describes the impact testing of structures in which a structure is struck by an impactor associated with a force transducer the output of which is related to the force which the transducer experiences on impact and encompasses a frequency range including the lowest frequencies which that force contains to any substantial degree. The impactor may be driven by an electromagnetic arrangement. The maximum amplitude indicates whether the structure is faulty or not.
U.S. Pat. No. 4,217,614 describes apparatus for automatically applying pressure sensitive labels to objects which utilises an application device in the form of a bellows which is pressure/vacuum operated in order to extend and contract the bellows in a label applying operation.